1. Field of the Invention
This invention relates to a method for preparing bonded stretchable nonwoven fabrics comprising multiple-component fibers. Nonwoven fabrics prepared according to the method of the current invention have an improved combination of elastic stretch, textile hand and drape.
2. Description of Related Art
Nonwoven webs made from multiple-component filaments are known in the art. For example, U.S. Pat. No. 3,595,731 to Davies et al. (Davies) describes bicomponent fibrous materials containing crimped fibers which are bonded mechanically by the interlocking of the spirals in the crimped fibers and bonded adhesively by melting of a low-melting adhesive polymer component. The crimp can be developed and the potentially adhesive component activated in one and the same treatment step, or the crimp can be developed first followed by activation of the adhesive component to bond together fibers of the web which are in a contiguous relationship. The crimp is developed under conditions where no appreciable pressure is applied during the process that would prevent the fibers from crimping.
U.S. Pat. No. 5,102,724 to Okawahara et al. (Okawahara) describes the finishing of nonwoven fabrics comprising bicomponent polyester filaments produced by conjugate spinning of side-by-side filaments of polyethylene terephthalate copolymerized with a structural unit having a metal sulfonate group and a polyethylene terephthalate or a polybutylene terephthalate. The filaments are mechanically crimped prior to forming a nonwoven fabric. The fabric is rendered stretchable by exposure to infrared radiation while the filaments are in a relaxed state. During the infrared heating step, the conjugate filaments develop three-dimensional crimp. One of the limitations of this process is that it requires a separate mechanical crimping process in addition to the crimp developed in the heat treatment step. In addition, the process of Okawahara requires the web or fabric to be in continuous contact with a conveyor such as a bar conveyor or a pre-gathering slot along spaced lines corresponding to the bars in the bar conveyor or lines of contact where the web contacts the gathering slot, as the product is shrunk or prepared for shrinking. Processing through a pre-gathering slot requires the use of cohesive fabrics that are pre-integrated and cannot be used with the substantially nonbonded nonwoven webs that are used in the current invention. Multiple-line contact with a bar conveyor during the shrinkage step interferes with fabric shrinkage and crimp development, even when the fabric is overfed onto the conveyor.
U.S. Pat. No. 5,382,400 to Pike et al. (Pike) describes a process for making a nonwoven fabric which includes the steps of melt-spinning continuous multiple-component polymeric filaments, drawing the filaments, at least partially quenching the multiple-component filaments so that the filaments have latent helical crimp, activating the latent helical crimp, and thereafter forming the crimped continuous multiple-component filaments into a nonwoven fabric. The resulting nonwoven fabric is described as being substantially stable and uniform and may have high loft.
PCT Published Application No. WO 00/66821 describes stretchable nonwoven webs that comprise a plurality of bicomponent filaments that have been point-bonded prior to heating to develop crimp in the filaments. The bicomponent filaments comprise a polyester component and another polymeric component that is preferably a polyolefin or polyamide. The heating step causes the bonded web to shrink resulting in a nonwoven fabric which exhibits elastic recovery in both the machine direction and the cross direction when stretched up to 30%. Since the length of fiber segments between the bond points varies, pre-bonding of the fabric prior to shrinkage does not allow equal and unimpeded crimp development among all of the bicomponent filaments since the shrinking stresses are unequally distributed among the filaments. As a result, overall shrinkage, shrinkage uniformity, crimp development, and crimp uniformity are reduced.
U.S. Pat. No. 3,671,379 to Evans et al. (Evans) describes self-crimpable composite filaments that comprise a laterally eccentric assembly of at least two synthetic polyesters. The composite filaments are capable of developing a high degree of helical crimp against the restraint imposed by high thread count woven structures, which crimp potential is unusually well retained despite application of elongating stress and high temperature. The composite filaments increase, rather than decrease, in crimp potential when annealed. The filaments are described as being useful in knitted, woven, and nonwoven fabrics. Preparation of continuous filament and spun staple yarns and their use in knitted and woven fabrics is demonstrated.
While stretchable nonwoven fabrics from multiple-component filaments are known in the art, there exists a need for a method for producing uniform stretchable nonwoven fabrics from multiple-component filaments which have an improved combination of uniformity, drape, and stretchability and which also have high retractive power without requiring a separate mechanical crimping step.